Gear pump having a rotor shaft integral with the crown gear



Jan. 2, 1968 y o. ECKERLE 3,361,074

GEAR PUMP HAVING A ROTOR SHAFT INTEGRAL WITH THE VCROWN GEAR Filed Oct. 15, 1965 INVENTOR OTTO ECKERLE ATTORNEY.

United States Patent 3,361,074 GEAR PUMP HAVING A ROTOR SHAFT INTEGRAL WITH THE CROWN GEAR Otto Eckerle, am Bergwald 3, Malsch, Kreis,

Karlsruhe, German Filed Oct. 15, 1965, Ser. No. 496,508 Claims priority, applicatignstiirmany, Jan. 15, 1965, 7 Claims. (Cl. 103-126) This invention relates to a gear pump and rotor and to the process for forming the rotor.

In summary, the gear pump rotor of this invention comprises a surface harden-able steel rotor shaft and an extrusion molded steel crown gear having a carbon content lower than the rotor shaft being attached thereto. The rotor is formed by welding the rotor shaft to a steel billet having the requisite carbon content, extrusion molding the billet to form a crown gear, preferably with an extrusion die having an axial point, and then removing surplus metal from around the teeth of the crown gear. The hob curves of the pin teeth of the crown gear correspond exactly in shape to the trochoid surfaces of the bevel gear surrounded thereby.

In modern manufacturing methods for forming rotors having crown gears, the crown gear is no longer formed by milling. Instead, the crown gear is cold formed by extrusion molding techniques, giving rise to difiiculties caused by the material used.

To provide wear resistance, it is necessary to harden the surface of the rotor shaft by induction. Therefore, the rotor shaft must consist of steel having a high carbon content of, for example, 0.6% which can be easily surfacehardened. However this material cannot be extrusion molded. For extrusion molding the crown gear steels can be employed having a maximum carbon content of 0.35% a sufficient hardening being obtained by the cold working of the extrusion molding process.

Since a material of low carbon content cannot be hardened without a previous carburization, a compromise material is usually selected, this compromise either impairing the quality of the rotor or requiring additional process steps.

The method and product of this invention avoid the above-mentioned difficulties. According to this method, a surface-hardenable rotor shaft consisting of a steel having a higher carbon content is combined, in a butt welding or friction welding operation, with a billet or semifinished steel slab having a lower carbon content. The billet is then extrusion molded to a gear wheel, for example a crown gear, in a conventional manner in a matrix, using the extrusion molding method. The shell of excess steel formed around the teeth is then removed.

The described method can be employed in connection with a gear pump having any conventional teeth arrangement and is particularly advantageous, for example, in connection with gear pumps with internal gears having trochoidal teeth. These pumps are distinguished chiefly by the fact that the crescent-shaped packing normally required in case of geared pumps having rotors with internal teeth is omitted. In the known pumps of this type, the pump gearing consists of a driven internal gear having inside teeth and a bevel gear or pinion having external teeth which mesh with the internal gear teeth. In the tooth gaps of the internal gear, bores are provided through which the conveyed medium is drawn into the internal gear or forced out of the internal gear. Apart from the fact that the fore relationships at the inside and the outside of an internal gear are not perfect, the bores represent hydraulically detrimental spaces which must be avoided. Furthermore, the hob curves of the internal gear teeth, starting from the circular arcs corresponding to the 3,361,074 Patented Jan. 2, 1968 shape of the bevel gear teeth, cannot be manufactured in their ideal shape by milling so that there are also dead spaces between the teeth.

In order to avoid the above disadvantages, it is the object of this invntion to replace the internal gear by a driven crown gear with pin teeth, the external diameter of this crown gear being approximately equal to the diameter of the bevel gear and to the height of a pin tooth. The hob curves of the pin teeth correspond exactly to the trochoid of the bevel gear and the lateral edges of the pin teeth form, in the region of the tooth gaps, an acute angle with the surrounding cylinder. The crown gear is manufactured by the extrusion molding process.

By the use of a crown gear, flawless force relationships are achieved on the inside and on the outside of the pin teeth. The chosen diameters,'in connection with the exact hob curve of the pin teeth, prevent the creation of dead space. The extrusion molding process is suitable for producing a crown gear whose teeth are provided with a flawless hob curve.

In the drawings, embodiments of the pump drive of the invention are illustrated.

FIG. 1 shows a rotor shaft and billet.

FIG. 2 shows the billet and rotor shaft bonded thereto positioned within a female die preparatory to extrusion molding with a male die.

FIG. 3 shows the extrusion molded crown gear prior to removal of surplus material from around the pin teeth.

FIG. 4 shows the crown gear in combination with a hardened insert having peripheral teeth which fit between the pin teeth of the crown gear.

FIG. 5 shows the assembly of a bevel gear and the crown gear.

FIG. 6 shows an enlarged view of the crown gear.

FIG. 1 shows the rotor shaft 1 and the billet 2 for the crown gear. Both parts are welded together and the weld seam 3 is removed by grinding or by turning on a lathe. The billet is shaped on a lathe at the outer circumference and at the vertical rear surface 4. Subsequently, the rotor is inserted in a female die 5, as shown in FIG. 2, and the male die 6 is pressed against the billet, whereby the material of the latter flows. An axial point 7 is provided on the die 6, ensuring a better flow of material from the center of the billet. In this manner, the crown gear 8 shown in FIG. 3 is produced, the pin teeth 9 thereof being surrounded by a shell 10 which is subsequently removed by lathin-g or grinding.

A punched, and if desired hardened and lapped disk 11, is bonded or brazed into the crown gear 8, as shown in FIG. 4. This disk is provided with teeth at its circumference which fit into the tooth gaps of the crown gear. Thereby, any curves or radii 12 at the corners of the transition of the tooth flanks to the bottom surface 13 of the crown gear are covered.

Furthermore, the lifetime of the rotor is increased since the disk 11 can have a greater hardness than the crown gear 8, and the butting face 14 for the bevel gear does not become too rapidly worn.

The gear according to FIGS. 5 and 6 consists of a driven crown gear 21 and a bevel gear 22 with trochoidal toothing meshing with the internal gear. The bevel gear is rotatably mounted on an axle 23. The outer diameter d of the bevel gear plus the height h of a pin tooth 24 is approximately equal to the outer diameter D of the crown gear 21. The flanks 5 and 6 of each pin tooth form, with the surrounding cylinder 7 at the tooth gaps 8 an acute angle or of, for example, 60. The crown gear 1 is welded to the drive shaft 9, the shaft being made of a surfacehardena-ble steel, and the crown gear being made of a steel having a lower carbon content than the steel of which the shaft is made.

It is obvious that it is also possible to manufacture, by means of the present process, rotors having a normal gear or an internal gear.

Obviously, many modifications and variations of the invention as hereinabove set forth can be made without departing from the essence and scope thereof, and only such limitations should be applied as are indicated in the claims.

The invention claimed is:

1. In a gear pump, a rotor and a bevel gear surrounded thereby, said rotor comprising a surface hardenable steel rotor shaft, an extrusion molded steel crown gear having a carbon content lower than the rotor shaft being attached thereto, said rotor shaft integrally fixed to said crown gear.

2. The gear pump of claim 1 wherein a hardened steel disk, having peripheral teeth fitting into the tooth gaps of the crown gear, is attached to said crown gear.

3. The gear pump of claim 1 wherein the crown gear has been formed with an extrusion die having an axial point.

4. The gear pump of claim 1, the outer diameter of the crown gear being substantially equal to the sum of the outer diameter of the bevel gear and the height of the pin teeth, the hob curves of the pin teeth having the shape of the trochoid of the bevel gear, and the lateral edges of the pin teeth forming an acute angle with respect to the cylinders surrounding the rotor.

5. A rotor for a gear pump comprising a surface hardenable steel rotor shaft and an extrusion molded steel crown gear having a carbon content lower than the rotor shaft being attached thereto.

6. The pump rotor of claim 5 wherein a hardened steel disc having peripheral teeth fitting into the tooth gaps of the crown gear is attached to said crown gear.

7. The pump rotor of claim 5 wherein the crown gear has been formed with an extrusion die having an axial point.

References Cited UNITED STATES PATENTS 1,380,250 5/1921 Reymond 29159.2 1,486,835 3/1924 Hill 230141 1,847,926 3/1932 Chase 29159.2 2,126,200 8/1938 Linderman 29-1592 2,302,907 11/1942 Eilers 103126 2,713,277 7/1955 Kaul 29--159.2 2,822,760 2/1958 Schirmer et al. 103126 3,298,219 1/1967 Schober 29159.2

DONLEY J. STOCKING, Primary Examiner.

WILBUR J. GOODLIN, Examiner. 

1. IN A GEAR PUMP, A ROTOR AND A BEVEL GEAR SURROUNDED THEREBY, SAID ROTOR COMPRISING A SURFACE HARDENABLE STEEL ROTOR SHAFT, AN EXTRUSION MOLDED STEEL CROWN GEAR HAVING A CARBON CONTENT LOWER THAN THE ROTOR SHAFT BEING ATTACHED THERETO, SAID ROTOR SHAFT INTEGRALLY FIXED TO SAID CROWN GEAR. 